Application of dry sludge of waste water treatment plant as aggregate in concrete production

Albourz Industrial City's wastewater is mixing of domestic and industrial wastewater. Nowadays because of prevent of Environment Protection Agency for hygienic bury, the most important problem is storing sludge in treatment plant zone. Present work has been performed to eliminate mentioned sludge through application in concrete materials. To characterize dry sludge, it was analyzed by XRD and XRF methods for crystalline phases and chemical compound. The results indicated the existence of more than 50 percent silica (SiO2), in Quartz crystalline phase, in the sludge. Also, the existence of more than 20 percent organic matter in the sludge was indicated. These organic maters will cause decrease in concrete mechanical properties. Therefore, a heating process to 650 oC was designed for dry sludge before application in concrete. The results of XRD analysis of cooked sludge analyze showed changes in crystalline phases. Considering the changes in crystalline phases, made it possible to create pozzolanic activity in material. To investigate pozzolanic activity STA analyze was performed. The result confirmed lack of pozzolanic activity in cooked sludge. To investigate dry sludge effects on concrete properties as aggregate, two mix designs of concrete at water to cement ratios of 45 and 55% and used sludge percentages of 0, 5, 10, 20 and 30% was selected. To investigate the sludge effects on concrete performance, compressive strength test was considered as durability index and specimens tested after 3, 7, 28 and 90 days of curing. The results indicated that in 90 days cured specimens containing 5, 10 and 20% dry sludge, compressive strength decrease about 4, 8 and 22% in comparision to control specimens (concretes without sludge). Due to huge application of concrete in Iran, and on the basis of low decrease in compressive strength (which can be acceptable), therefore, it will be possible to use concrete with 5 or 10 percent of sludge for each type of application. Also, the application of 10 and 20% dry sludge is possible only for pavement concrets.